Means for controlling the air supply in furnaces and like heating appliances



Dec. 22, 1953 M. w. THRING ETAL 2,663,272

MEANS FOR CONTROLLING THE AIR SUPPLY IN FURNACES AND LIKE HEATING APPLIANCES 4 Sheets-Sheet 1 Filed Feb. 21, 1948 Dec. 22, 1953 M w THRING ETAL 2,663,272

MEANS FOR CONTROLLING THE AIR SUPPLY IN FURNACES AND LIKE HEATING APPLIANCES Filed Feb. 21, 1948 4 heet -rSh a 2 Dec. 22, 1953 M. w. THRING EI'AL MEANS FOR CONTROLLING THE AIR SUPPLY m FURNACES AND LIKE HEATING APPL IANCES 4 Sheets-Sheet 3 Filed Feb. 21, 1948 IIIIIIIA III4 Dec. 22, 1953 M. w. THRING EI'AL 2,663,272

MEANS FOR CONTROLLING THE AIR SUPPLY IN FURNACES AND LIKE HEATING APPLIANCES Filed Feb. 21, 1948 4 Sheets-Sheet 4 fw .HJ PI\ Patented Dec. 22, 1953 MEANS FOR CONTROLLING THE SUPPLY 1N FURNACES AND LIKE HEATING AP- PLIANCES Meredith Wooldridge Thring and Fritz Bruno Karthauser, London, England, assignors to C. U. R. A. Patents Limited, London,,England Application February 21, 1948, Serial No. 10,056

6 Claims.

This invention relates to means for controllin the supply of air for combustion of solid carbonaceous fuel in furnaces and like heating appliances of the kind described in U. S. appln. Ser. No. 507,850 (now U. S. Patent No. 2,515,545).

In that specification is described a furnace or like heating appliance in which the rate of heat release and the composition of the combustion gases are independently and simultaneously controllable at will. One form of the heating appliance comprises a hearth, means for feeding solid fuel thereto to maintain thereon a stable combustion bed of fuel having a free surface, means forming a passage for conducting to a zone of use the combustion gases passing from the said free surface, air-jetting apparatus constituting the sole means for supplying combustion air to the said bed and comprising an inlet opening arranged to project the whole of the air for combustion against the said free surface so as to penetrate into the bed therethrough and also comprising means, for example, a fan or blower, for regulating the quantity of air supplied in unit time to establish a definite rate of combustion in the bed, and a regulating device for varying the effective cross sectional area of the said inlet opening for maintaining the pressure therein, and correspondingly the velocity of impingement of the jetted air on to the free surface, at a predetermined value independently of the quantity supplied in unit time.

. In operating the appliance the rate of heat release is controlled by controlling the rate of air supply, that is to say the quantity of air supplied in unit time,'and the composition of the combustion gases at or near the fuel surface is controlled by controlling the velocity of impingement of the jetted air on to the free surface, whereby the mean penetration of the jetted air into the fuel bed and consequently the composition of the combustion gases is controlled. Thus, it is possible so as to adjust the mean penetration of the jetted air that the combustion gases contain oxygen and combustible products, more especially carbon monoxide, in proportions relatively to one another requisite for their substantially complete conversion into fully burnt products outside the fuel surface, whereby a maximumliberation of heat for a given rate of air supply, and consequently very high temperatures, are attained. Alternatively, the mean penetration can be increased beyond this point to give combustion gases containing a higher proportion of combustibl products relatively to oxygen, or it can .be decreased to give combustion gases containing a lower proportion of combustible products, and

therefore an excess of oxygen.

The regulating device for varying the effective cross sectional area of the inlet opening may be, for example, an adjustable valve for partially obstructing the said opening. Any variation in the rate of air supply, in the absence of any other adjustment, will lead to a change in the pressure of the air in the air-jetting apparatus between the fan or blower and the inlet opening or nozzle. Consequently, when it is desired to alter the rate of heat release by varying the rate of air supply, without alteration of the mean penetration of the air jet into the fuel, an increase in the rate of air supply will necessitate an increase in the effective cross sectional area of the inlet opening in order to maintain the velocity of the air jet substantially constant; and conversely, a decrease in the rate of air supply will necessitate a decrease in the said cross sectional area. Accordingly, two separate adjustments have to be made.

However, the velocity of the air jet emerging from the inlet opening into the furnace is in a general sense a function of the pressure of the air in the air inlet opening. Thus, if the said pressure is maintained constant, the velocity of the jet will also remain substantially constant.

It is an object of the present invention to provide in a heating appliance of the kind described in the aforesaid application Serial No. 507,850 (now U. S. Patent No. 2,514,545), means for automatically maintaining the pressure of air in the said air inlet opening constant or approximately constant when variations are made in the'rate of air supply. To this end the two adjustments referred to above are coupled together, and this increases the efficiency of the heating appliance and makes it more suitable for purposes in which it is important to control the composition of the combustion gases.

According to this invention, in a heating appliance of the kind described above there is provided detecting means responsive to variations of pressure in the said inlet opening due to variations in the quantity of air supplied in unit time, and means controlled by the said detecting means for operating the said regulating device to restore the pressure to substantially the predetermined value.

The detecting means responsive to variations of pressure in the air inlet means may take the form of a member capable of displacement by pressure variations in the air inlet means on either side of a mid-position which the member stem occupy its mid-position at different pressures.

Such regulating means may, for example, take the form of adjustable weight or'sp'ring loading means acting on the displaceable member. The regulating means may be marked or calibrated in terms of the pressure which it"is'desird'to' neurtain, or, since the pressure is in a general sense a function of the velocity of the all" from the inlet opening, in terms of this velocity:

Since the velocity, when other factors are the same, determines the composition of the ctmbu's tion gases, the said marking or calibration may be-i'n'" tel-meet the compesition of the combustion gases, provided that other combustion conditions, suc'h as the nature:- of the fuel and the form and porosity of the" fuel bed; are not likely" to be changed to any considerable extent.

The" displa'ceable member may be mechanically connectedtothe devicefor regulating the inlet opening so" as to operatethe saiddevice-directly,

provided that the movements of the displaceable member under action of pressure changes' are sufliciently powerful for the purpose; Alterna' tiv'ely;.the displacea'ble member may control the operationof' thesaid regulating device by controlling asupplyrof energytoactuate-indpend ent means for operating the regulating device: Thus; for example, the displaceable" member may control the admissionoffluid under pressure to acylinderto move a-- piston therein connected" directly to the regul-at-ingvdevice; or it may control the supply of-electric current to electrically opera-ted means for actuating the regulating-device. In the latter case the-displaceable member may, for exalffi'ple operate a directcurrent reversing switch to change the direction of rotation of a dirct'current electric-motoradapted to move the g. device in one direction: or the other I as'ing'or'de'creasingthe efiectiveareaof the inlet" opening; the switch being inoperative anc' a s'sing no current I displaceable mmbfis i i'r 'de i iqe. e beinee ie s when the-s 1d' member moves to one side or the otherofitsriiid positiofi. I

The pressure to which the detecting means is responsive may be the pressure" in" the air inlet means with re erend to" theatmosphe'ric pressure: When; however, material changes of ressure-are11ke1yto'cccur the" combustion" space lll'th' Vi'C iIiitYO'fUh 'e Sill iiiletthe' dtedtilflg means be respons ve 'to" the prssure'm the' air" inlet of the appliance: When'a plurality'of a irinl'ets" 's and" on the other to the is present each'inlet' may have a" device for r'eeii-t lating the effective area: of its opening and also.

operation can be with pressure responsive detecting means to control the operation of the regulating device or a single such detecting means may be used to conrol all the inlets or groups thereof.

In the case of a plurality of air inlets they may all be connected to a common air supply and cap'able of being separately closed and opened so as to vary the aggregatea'rea of the inlet open- .ings, for example, as described in British speification No. 12,376 of 1944 (now British Patent No: 587,821). In this; arrangement each inlet opening can be" regarded as a part of a single inlet opening constituted by the sum of the areas of all the openings, and the number of inlets in reased or decreased to restore the" desired pressure when the rate of supply of the air in the common air supply is increased or decreased. In this case the regulating device may consist of valves provided in the several inletsfo'r completely closing or completely opening the same each independently of the others or in group'sof two orore inletsf independently o f other groups: Wrt this" arrangement single detecting means be provided responsive'to variations of pressure in the common ai-rsupply, and the said detecting means may control the closing and-opening of; the valves of the air or of groups of air" inlets insucce ssion until the desired pressure been" restored. For this" purpose there may be used as a displaceable'member an electrically conductive liquid} such as mercury, in a manometer tube, the liquidin one limb of the tube being subjct'to the pressure inthe common air supply and in the other limbfto' atmosphericpressure or to the pressure the combustion space in'the-vicinityof the-air inlets;

Each limb of the manometer tube is" provided with" an electric contact" order to 'control le trical means,- for example, solenoids, for succe's siv ely opening or closing the valves so long as the'liquid inthe" manometer tube make's contact with one or other or the contacts therein.

Various clmstrueti'ons' or automatic chatter means in' accordance with the invention-are'illus trate'd mth' accompan ing drawings,- in which:

Figure 1 is alongitudinal section of-one'c'o1r-'" struction of a homeredate with pressurere sponsiv'edeteoting meaflsy Figure 2 is a similar sectionof another eta-:- stru I I I II Figure 3 is a similar" seti'onof, a further con-" struction, and I I I I I I Figure 4 shows ,i'agrammatic form a further construction of ureresponsive detecting meet I and means rarcontrolling a plurality of nozzles. I

Figures; sn'qws; rliseeticfiaii elevation far-mes provided withautomatic' control means of the kin'd'shown nFigure 3'.) I I I I I I In the s v era'lfigurs like reference numter's areI'u'sec l to denoteilike parts; II I I In Figures 1, 2 and 3, a no'ziz le IO is opening II- i Suppl-1 dwitlr ir through a pipe; r2

by rhear s off-anIor 'blo er (pot pews); The effective area of the n leopening H is' c trolled by means offaf'valve l3 which is movable In Figure 1 the hollow' valved} is fixedto one end atubel i to which is fixed near" the other end thereof a piston 1 i'rnovable withina hambr' it; I 'r t be at; s maintained in an axial pest tionwithinfthe nozzle lilfby' means of four pins l'l of which only two" are shown) projecting radially inwards from; the inside of noz zle li0'. Thetub M" is made" hOIIOW iII O Idi" tht the" progress of combustion can be observed from the exterior of the furnace.

The righthand side of the piston I5 is acted on by the air pressure within the nozzle I and pipe I2 communicated to the piston through an opening I8 in the chamber I6, and. on the other side the piston is acted on by a, spring I9 compressed between the piston and a housing 26 formed in the cover 2I of the chamber I6. On the same side the piston I is also exposed to atmospheric pressure by means of the opening 22 in the cover 2|. The sizes of the openings I8 and 22 are sufiicient to enable the piston I5 to respond rapidly to changes in the air pressure acting upon it, but are also small enough to reduce by damping the tendency for the piston to oscillate or hunt when it moves in response to a change in pressure. A regulating screw 23 enables the degree of compression of the spring I9 to be regulated.

The movement of the piston I5 is communicated directly to the valve I3 by the connecting tube I4, and the position of the piston and the valve depends on the air pressure in the nozzle I3 and pipe I2 and the counterbalancing pressure of the spring l3 and of the atmosphere. Thus, for any given setting of the regulating screw 23, an initial increase or decrease or pressure in the nozzle caused by altering the air supply rate will move the piston to the left or right, respectively, and so cause an alteration in the effective cross sectional area of the opening II sufficient to restore the pressure to approximately its original value for the altered rate of air supply. By changing the setting of the regulating screw 23 the pressure which it is desired to maintain in the nozzle can be altered. It will be understood that, owing to the increase in the force required to balance the pressure of the spring I9 as it becomes more compressed, the air pressure cannot be restored to exactly its original value. However, by using a spring of suitable characteristics it is possible to arrange that an approximately constant pressure adequate for practical purposes is maintained.

In the construction shown in Figure 2, the nozzle Ill has an opening I I in the form of a rectangular slot, and the valve I3 takes the form of a tongue movable across the opening II to vary its effective area. The tongue I3 is provided with a plate 24 to which is attached a rod I4, the plate 24 also serving to maintain the tongue I3 in position within the nozzle I0. At the other end of the rod I4 is fixed a piston 25 movable within a cylinder 26. The piston is moved by a fluid under pressure, such as oil, introduced into the cylinder on one or other side of the piston as hereinafter described. The air pressure in the nozzle I6 and inlet I2 is communicated through a duct 21 to the lower side of a diaphragm 28 mounted in a chamber 29. A spring 3!] acts on the upper side of the diaphragm 28, and the latter is also subjected on that side by means of a narrow tube 3| to the pressure prevailing in the furnace in the vicinity of the'nozzle opening I I. The pressure exerted on the diaphragm 28 by the spring 30 is so adjusted by means of a regulating screw 32, which'can be locked by a nut 33, that the diaphragm assumes substantially its midposition under the counterbalancing pressure which it is desired to maintain in the nozzle I0.

To the centre of the diaphragm 28 is fixed a cylindrical slide valve 34 movable within a bore 35. The slide valve 34 comprisesa central 'por--" tion of reduced diameter between two blocking members 36 and 31, of full diameter, and two further portions of reduced diameter on the other sides of the members 36 and 31. The member 36 controls a duct 36 for admitting fluid under pressure into the cylinder 26 on the lefthand side of the piston 25, and the member 31 controls a duct 39 for admitting such fluid into the cylinder 26 on the other side of the piston. The fluid is introduced through a duct 40 into the space between the members 36 and 31, but is unable to enter the cylinder 26, when the diaphragm 26 and valve 34 are in the mid-position, since the ducts 38 and 33 are then closed by the members 36 and 31, respectively. When the pressurein the nozzle I 0 increases or decreases due to a change in the rate of air supply, the diaphragm 28 and with it the valve 34 moves up or down, respectively. An upward movement of the valve 34 causes the member 31 to open the duct 33 and the member 36 to open the duct 38, thereby enabling fluid to pass from the duct 40 through the duct 39 into the cylinder 26 on the righthand side of the piston 25, and also enabling fluid to pass from the other side of the piston through the duct 36 and into a duct 4I communicating with a duct 42 for the discharge of the fluid. Accordingly, the piston 25 moves to the left and carries with it the tongue I3 to increase the elfective area of the opening I I. As the pressure falls in the nozzle I0 the diaphragm 28 and valve 34 will descend, and when the pressure is restored to the original value the diaphragm and valve will have reached the mid-position in which the flow of fluid to and from the cylinder 26 is shut off by the blocking members 36 and 31. The piston 25 and tongue I3 are thus locked in their new position. A downward movement of the diaphragm 28 and valve 34, due to a decrease in pressure consequent upon a reduction in the rate of air supply, again causes the members 36 and 31 to open the ducts 38 and 33, but in this case the duct 36 is put into communication with the supply duct 40 and the duct 33 into communication with a duct 43 which in turn communicates with the discharge duct 42. Thus, fluid is introduced into the cylinder 26 on the lefthand side of the piston 25 and discharged from the cylinder on the other side of the piston, which therefore moves to the right to reduce the effective area of the opening I I. When the pressure in the nozzle increases to the original value the diaphragm 28 and valve 34 will return to the mid-position, and the piston 25 and tongue I3 will be locked in their new position.

The supply of fluid under pressure used to operate the piston 25 may advantageously be derived from some source associated with the furnace or other heating appliance. ple, if the furnace is part of a steam generator, the duct 40 may be connected to the boiler feed pump. Alternatively, if the furnace is part of a transportable steam boiler unit of the kind described in British specification No. 12,376 of 1944 (now British Patent No. 587,821) fitted to a vehicle, the duct40 could be connected to a high pressure oil lubricating system on the vehicle.

In the construction shown in Figure 3, the nozzle I 0, opening II and tongue I3 are similar to those shown in Figure 2. The rod I4 is similarly connected at one end to the plate 24 of the tongue I3, but its other end is screw-threaded as shown at 50. On the screw-threaded portion gear 52 driven by a direct current electric motor For eXam- '53. The pinion 5| is seciiiied against aerial movement along "the i'fibitiii 50 "of the -ic'id H Betifieh a hearing 5'! anti a bush hiifihw-hich v bush the portion 50 6f the iod tree to taste longitudinally.

The pressure responsive detecting ih'ahs 66hsists of an invehted 'bell BB floating in ah oill hath 51. The ihterii Of thhliifi is Qo'ffifniinif tion With the pi'es slii in the pipe 1'? m'ihs of a conduit 58. weight (if the beil'ieqifi'i ii to counterbalance the prssii r which it is 'aesiie'e t mal'htaih in the inlet 12 ad jlistahle lif hi'aii's of detachable Weights 59. At the top of the bell 56 is connectd a switch 60 which t'iirh's upon a fiked piVbt 5| ahd carries a flail 0f chht'act plates 62 and '53 adapted t6 make and reak bon tact with a pair er 'fiiied eoiiteet plates :54 and 65. The other end Of the am 60 em-f es a 60in tact es adapted to engage the "or other ''f We centa'ets B1 and B8. The fiiifafits 62; 63 M and 65 constitute a Switch $61 r''ViSi'I'l'g dir'tih of the current suppiieii item a battery 6!; to new Winding bf the elfitfi'c mptdr 53-; The lids 10 Supply curfe'i'it t6 the field Winding; the ieees H supply current to the armatur winging. The leatis' 70 are cnn'ect'ee to the and 65 so that the aire'eti'oii o theeu ent energiSihg the field Winding be f've e While the leads 1| are permanently eo'mie ed to e e th and the content as so that the eminent meet me 30 the armature winding always news in the ame direction. Whe'ri the bell is its iii p 'hst position contest 55 engages contact ET, (:0 i'iladt ea engages contact 6'4, and tent-est engages contact 65. In this hesition, therefhre; the den tact 64 is connected tii the pesitive pele" (if the battery 59 arid the COhtaCt 65 is hcihtl'ietd t6 the negative DOle' thrb'u'gli the earth 'th lled 12 connected to the cbritact 62'. Ccnv'ei sei'jy iii the lowermost positiijri bf the bell the 'c ifl'i'itht 66 engages contact fia c'ontaet GS Iig'QJgeschhtEct es, and contact 62 engages contact s4, s6 that ebntaet 64 is then eoniie'eted to the negative eie' and eonteet 65 to the positive iible; thus re siiig the direction of the current in the new win ing. ,i

The skiiit 'O'f the [561156 iss'iiffiiiiei'itlj n ght 136 ensure that when a slight change of pressure dGC'iilS iii the pipe [2 thebell will Eoi'itiiiue i isle 01- fall mitntiie eeiit'ie'ete B6; s1 0? as; ea eii'e' hose-e; and th tt-tiie ten will return ta its; orig ta subste tietiy' itseneiiie viii-lie. v V H eneeq ei iii-p'ositi'oii r the' b'eil iie eiir'rer'it s su piiee to the meter" 53; When an iiieieeee in pressure in the ipei2 occurs due to an increase in the rate of air mitt-1t, the beii as'eiid's uppermost posit on st that the inotbr is gized to drive" it the" direction rei'iuireii td retract the tciiigiie 13 and s'ii'infifte the eiee, of the nozzle opening H. l A reduction in fires:- sure in thep'ipe 12, on the" other' liand, cans'e s the bell to descended that the IIiOtiiI is driv fiiii the reve'ise diiiitiofi to adifance th L3 and so re'du ce the tree; of the nozzle opening H;

both eases, fifessuite has been restored to suhstaritialli its original value by the adjustment of the opening II, the bell 56 Will return to its mid-position in whichthe centact 5Q is not toiiching either'of the cent-acts 161 and 88. By changingfthe; weightsjl! onthe beii the pressure which it is desiredto maintain) in the nozzle-can be altered, The sensitivity of the device depends on thejightness in weight of that portion of the skirt of the bell which moves into and out of the oil dui ing changes in the air piessifi; I V I In the construction shown in Figure 4-, there is fil'urality 6f idds l l; of which 61115? twb mer ted i4 and Mix er shown, and each of whicheontrols neof e plurality "6f nozzles (not shqwn) connected ti a c'm'n' o'n air supply inain. Each ro'd. Hi operates a 'v'aii e (not shown whereby the air-supply to the respective nozzle can be either fu ly admitted or completely 's'hut offv Thus, the aggregate 'a 'i'ea of the nozzles in 'o'peratioh can be varied. to 'iha-intain an approximately constant lfiies sifi the Operative nozzles when changes ate In'a'gie in the rate or "air supply. The arrangement of nozzles and valve may be simi ar to that shown ii Figures 2 an 3 'of British specifi'cation N6, 12,376 of 1944 (how British Patent NO. 587,821);

THe-pfesi1re rsponsiv '(itctin'g means con SiS tS Of '2; u ttflfie all "containing an electrically conductive liquid, for example, ineicury. One end '8] 6f the tubecjdrrim 'unieats With the con).- men air supply main between the fan or blower and the nc'zzies, and the other end 82 is in commiiiiiCatiQh with the combustibh space in the furnace in the vicinity of the nozzles. In the limbs 83 the at ti the tube iii) are provided contests 85 and 315, respectively. The t eltidal distense between these dli'tac'ts Cai'h be Varied by adjusting the tilt of the tube 80 by means of a set screw 3'? against which rests an abutment 88 at the bottom Of the tune 80. This vertical dis tahce is so adjusted that when the pressure in the supply main is at thev'alue which it desired to maintain, the liquid in the tube occupies a mid-pi'sition in which it does not make contact with either of the contacts '85 eta When en increase iii the rate of air "supply causes an incieei'se in pressure in the'suppl'y main, the liquid the 'lirhb8'3 rises until it reaches the contact 35, thus closing the circuit "of a sole- 1101a @Qfrom 5, battery iifith'rough leads 9| and 92, the lower ccntacts "of a switch 93 anii to the battery through the earth. When thus ener gisd, the 'sol'enoid 89 jat't'racts an armature 94 connected to the rod M, which is thus pulled to the left to open the valve of the nozzle controlied thereby. At the end ,of its travel the armature 9'5 operates the switch 93 by means of a mg 95 st as to open the lower pair of contacts time the upper pair of contacts. In this manner the circuit of the solenoid '89 is broken, and the cuirent divertedthrough a lead 96 and the lower contacts (when closed) of a'switc'h 93a to iiergise a "solenoid 8911, which attracts an armature Mu connected to a second rod I ia which opens the valve of a further nozzle. If, however; during the opening of the first Valve controlled. by the rod T4 such a reduction in pressure in the airgsupply i'nain occurs that the liquid inthe tube '30 returns to its mid-position and breaks the battery circuit, the solenoid 39a will not he energised and the valve controlled by the rod Ma'wiil not be Opened.- 'It will be under-- stood that th'e'ie areiiurther solenoid units (not shown) each comprising a solenoid 89, switch 9.3, armature 9t and rod l4, and that if,- after the opening of the second vaii'ie controlled by the rod Me,- the battery "circuit is het broken by the liquid the tube t0, the succeeding units wi-lirbe operated in turn until the liquid returns to its mid-position.

When .i-eeiiietieii in the rate at air supply causes the pressure in the supply i'nai n to fail, the liquid in the/limb in rises until it readies the ture 94 and so pulls the rod I4 to the right to close the valve of the nozzle controlled thereby. At the end of its travel the armature 94 operates by means of a lug "30 the switch;99 to cut out the solenoid 91 and energise a solenoid 97a in the manner described in connection with the solenoid The solenoid units may, if desired, be so interconnected that the order in which the nozzle valves are opened is not the exact reverse of the order in which they areclosed. In this way amore even distribution of the combustion air over the fuel bed can be secured. If desired,.each rod I 4 may control more than one valve, and'the rods may operate the valves electrically.

It will be understood that the pressure respon- I sive detecting means and valve actuating means of the various constructions shown in thedrawings can be modified,'and are in many cases interchangeable. For example, a single rod I4 as shown in Figures 1, 2 or 3 could simultaneously operate a plurality of valvesor tongues I3 each in a separate nozzle, or could operate in succession a series of nozzle valves of the kind operated by the rods M, Ma etc. in Figure 4. An alternative means to that shown in Figure 4 for operating the radially arranged nozzle valves in the transportable steam generator shown in Figures 2 and 3 of British specification No. 12,376 of 1944 (now British Patent No. 587,821), comprises an actuating ring adapted on rotation in one direction or the other to open or close, respectively, the nozzle valves in succession, as is the sequential valve opener of U. S. Patent No. 1,630,977, issued May 31, 1927, to Smoot. For example, for every given number of degrees of rotation, say 2, in one direction or the other the actuating ring would open or close a single valve or a group of two or more valves. The ring could be operated by a single rod actuated by pressure responsive detecting means in the same manner as the rod It in Figures 1, 2 or 3.

In Fig. 5 is shown a furnace constructed in accordance with this invention. The furnace, which is constructed and operates in the manner described in United States Patent No. 2,515,545, comprises a refractory rear wall H8, hearth III, front wall H2 and roof H3 enclosing a combustion space H4 and fuel bed H5. naceous fuel is fed under gravity from a fuel hopper IIE to the fuel bed. The hopper H6 has a fuel charging opening I I7 at the top which is closed air-tight by means of a cover 8. The combustion gases issuing from the free surface N9 of the fuel bed H5 pass through a passage I29 to a zone (not shown) in which the sensible and potential heat of the combustion gases is utilized for some heating purposes, for example, for generating steam. The air for combustion of the fuel is directed in the form of a jet against the free surface of the fuel bed by means of a nozzle I ll of the kind shown in Figure 3, which is provided with a tongue I3 controlling the size of the opening, the tongue being moved by the rod I I I which is actuated by an electric motor 53 through the transmission means 50, 5|, 52 and 55 as described above. The motor is operated through the leads I0 and H by the pressure responsive means and electric contact means shown in Figure 3, the bell 56 shown in that figure being Solid carbo creases.

in communication with the pipe I2 through the conduit 58. Combustion air is supplied under pressure to the nozzle I0 through the pipe I2 by means of an electrically driven variable speed blower I2I. The quantity of air supplied to the fuel bed in unit time is controlled by regulating the speed of the blower I2 I as by means of a rheostat I22 connected in the leads I23 supplying current for driving the blower. When the speed of the blower is changed to increase or decrease the quantity of air so supplied, the pressure in the nozzle ill, and consequently the velocity of the air issuing from the opening ll, increases or de- The tongue I3 is moved automatically to increase or decrease the size of the opening I I by the control means shown in Figure 3, so as to restore the said pressure and velocity to substantially the value predetermined for maintaining a given extent of penetration of the air into the fuel bed and correspondingly a given composition of combustion gases issuing from the fuel bed, notwithstanding the change in the quantity of combustion air supplied to the fuel bed.

While there have been described herein what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art that minor, modifications and changes may be made therein without departing from the essence of the invention. It is therefore to be understood that the exemplary embodiments are illustrative and not restrictive of the invention, the scope of which is defined in the appended claims, and that all modifications that come within the meaning and range of equivalency of the claims are intended to be included therein.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. A heating appliance for the combustion of solid carbonaceous fuel comprising a hearth, means for feeding solid fuel thereto to maintain thereon a stable combustion bed of fuel having a free surface, means forming a passage for conducting to a zone of use the combustion gases passing from the said free surface, air-jetting apparatus constituting the sole means for supplying combustion air to the said bed and comprising nozzle means arranged to project the said air against the said free surface so as to penetrate into the bed therethrough and also comprising means for regulating the quantity of air supplied in unit time to establish a definite rate of combustion in the bed, a regulating device for varying the eifectivecross sectional area of the said nozzle means for maintaining the pressure therein at a predetermined value independently of the quantity supplied in unit time, detecting means responsive to variations of pressure in the said nozzle means due to variations in the quantity of air supplied in unit time, and means controlled by the said detecting means and operatively connected to the said regulating device for operating the latter to restore the pressure to substantially the predetermined value.

2. A heating appliance as claimed in claim 1, wherein the pressure responsive detecting means is a displaceable member subjected to the pressure in the nozzle means and displaced by variations in the said pressure on either side of a midposition which the member occupies when the pressure is substantially at the predetermined value.

3. A heating appliance as claimed in claim 2, wherein the means controlled by the displaceable 11 member for operating the regulating device is a mechanical connection. between thesaid member and device for operating the latter directly.

4. A heating appliance as claimed in claim 2,

wherein the means controlled by the displaceable member for operating the regulating device comprises a source of fluid pressure and a cylinder containing a piston operatively connected to the regulating device and actuated. by the admission to the cylinder of fluid, the admission of which is controlled by the displaceable member.

5. A heating appliance as claimed in. claim 2.. wherein the means controlled by the displaceable member comprises electrically actuated means operatively connected. to the regulating device and switch means. operated by the displaceable member and connected in. the circuit supplying electric current to the said electrically actuated means.

6. A heating appliance as claimed in claim5, wherein the electrically actuated means. is a direct current electric motor in driving connection with the regulating device for moving the latter to increase the effective crosssectional area of the nozzle means in one direction of; rotation of the motor and to decrease the said area in the opposite direction of rotation, and the displaceable member is, operatively connected to a direct current reversing switch.v connected inv the circuit supplying current to the said motor and operated by the displaceable member to reverse the current when the said, member ,movesfrom one side to the other side of its mid-position.

MEREDITH WOOLDRIDGE THRING. FRITZ BRUNO KARTHAUSER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 56,090 Patterson, July 3, 1866 7 180,330 Ebbinghaus July 25, 1876 265,348 'Tourangin. Oct. 3, 1882 581,970 Wheeler May 4, 1897 759,320 Schutte May 10, 1904 946,404 Shutts Jan. 11,1910 1,030,332 Rusby June 25, 1912 1,360,285 Gibson Nov. 30, 1920 1,551,272 Smoot. Aug. 25, 1925 1,879,342 Lauter Sept, 2'7, 1932 1,997,833 'Roland Apr. 16, 1935 2,083,046 Burke June 3, 193" 2,303,992 Frazer Dec. 1, 1942 

